1. Field of the Invention
This invention relates to a Ce.sup.3+ -containing glass composition for Faraday rotation elements. Since the glass of this invention is very stable and variations in composition due to volatilization are small as compared with conventional glasses containing Ce.sup.3+ for Faraday rotation elements, the glass of this invention can be produced easily in high yields.
2. Description of the Prior Art
Heretofore, glasses containing large amounts of paramagnetic rare earth element ions have been used as Faraday rotation elements because of the large Verdet constant of these glasses. Generally, rare earth element oxides other than cerium oxide are very expensive, and there is a great demand for relatively inexpensive glasses containing Ce.sup.3+ for Faraday rotation glasses. However, conventional Ce.sub.2 O.sub.3 -P.sub.2 O.sub.5 type glasses disclosed, for example, in Japanese Patent Publication No. 10132/77 (see Nos. 1 and 2 in the table to be given hereinbelow) are very unstable, and tend to devitrify at the time of melt-molding. Furthermore, since the volatilization of P.sub.2 O.sub.5 from this glass composition is marked, the glass composition tends to vary. Hence, the yield of such glasses is extremely low.